Plot
In 1945, near the end of World War II, kamikaze pilot Kōichi Shikishima lands his Mitsubishi A6M Zero for repairs at the Japanese base on Odo Island. Lead mechanic Sōsaku Tachibana deduces that Shikishima is feigning technical issues to flee from his duty. That night, Godzilla, a large dinosaur-like creature, attacks the base. Tachibana tells Shikishima to fire at the monster from his plane, but he panics, fails to shoot, and is knocked unconscious. When he awakes the following day, he finds Tachibana is the only other survivor, who is furious at him for failing to act.
Shikishima returns home to find his parents were killed in the bombing of Tokyo. Plagued by survivor's guilt, he begins supporting a woman, Noriko Ōishi, whose parents also died in the bombing, and an orphaned baby, Akiko, whom Noriko rescued. He finds employment aboard a minesweeper tasked with disposing of naval mines. Meanwhile, Godzilla is mutated and empowered by the United States' nuclear tests at Bikini Atoll; it destroys several American ships and sets off to Japan. Owing to tensions with the Soviet Union, the U.S. offers no help save for a few decommissioned Imperial Japanese Navy vessels approved by General Douglas MacArthur. The Japanese government, concerned about inducing panic, does not notify the public about the danger.
In May 1947, Shikishima and his minesweeper crew travel to the Ogasawara Islands and are tasked with stalling Godzilla's approach to Japan. They release a mine into Godzilla's mouth and detonate it, causing significant damage, but it quickly regenerates. The heavy cruiser Takao then engages Godzilla, but is destroyed when the monster unleashes its heat ray. After returning to Tokyo, Shikishima opens up to Noriko about his encounters with Godzilla at Odo. Days later, Godzilla makes landfall in Japan and attacks Ginza, where Noriko works. She narrowly survives the initial attack and reunites with Shikishima. Enraged by tank fire, Godzilla obliterates much of the district with its heat ray, killing tens of thousands. Noriko pushes Shikishima to safety, but is caught in the blast and presumed dead. Devastated by the loss, Shikishima vows revenge.
Former naval engineer professor Kenji Noda, one of the minesweeper's crew, becomes frustrated by the government's inaction. He devises a plan to destroy Godzilla by luring it out to Sagami Bay before surrounding it with Freon tanks and rupturing them, sinking the monster, and letting the resultant water pressure crush it. Should the plan fail, balloons will be inflated under Godzilla to force it back up, killing it through sudden decompression. To enact his plan, Noda has recruited navy veterans. Shikishima recruits Tachibana to repair a Kyushu J7W Shinden fighter. He plans to kill Godzilla in a suicide attack by flying into its mouth and detonating explosive charges on board. He leaves Akiko in the care of his neighbor Sumiko before Godzilla resurfaces.
As Shikishima lures Godzilla to the trap set by two destroyers, Sumiko receives a telegram intended for Shikishima. Godzilla survives the initial plunge and then breaks free before being forced back up, sustaining serious injuries from the resultant decompression-induced barotrauma. With the help of a fleet of tugboats organized by Mizushima, another crewmate from the minesweeper, the ships haul Godzilla to the surface. Enraged, Godzilla prepares to destroy all the vessels with its heat ray, but Shikishima crashes the plane into Godzilla's mouth and destroys its head. The crew celebrates as Shikishima ejects before the explosion and parachutes to safety, using an ejection seat that Tachibana installed in the Shinden, imploring him to let go of his guilt and continue living.
Upon returning home, Sumiko gives Shikishima the telegram, which leads him to a hospital where he reunites with Noriko, who survived the destruction. Meanwhile, a chunk of Godzilla's flesh begins to regenerate as it sinks into the ocean.
